Narcotics use has been identified as one of the major social problems of the twentieth century. Governments have sought to reduce the traffic of narcotics by intensive searching of vessels used to transport narcotics between countries. However, such search and seizure tactics have not yet succeeded in reducing the level of narcotics use.
The major impediment to search and seizure operations is the concealment of narcotics in containers or structural parts of a vessel. Often these containers or structural parts are made of metal or some other rigid material. Thus, searching for narcotics requires destruction of personal property which requires strong justification.
Accordingly there is a need for non-destructively detecting narcotics or other substances concealed behind barriers of metal or other rigid materials. A portable, hand-held detector would be particularly useful to conduct quick, non-destructive searching of vessels at ports of entry.
Various techniques have been proposed to detect substances behind metal and other barriers. One such system is described in U.S. Pat. No. 4,864,142. That system utilizes the well-known phenomena of neutron resonance scattering, i.e., that a particular nuclei has large neutron cross sections for a neutron beam of a particular resonance energy characteristic of the particular nuclei. In that system, a tunable neutron source provides a beam of nuclei having the resonance energy of a nuclei desired to be detected. The source used is described in the patent at col. 10, lines 29-70, and utilizes a proton beam to generate neutrons. Since the protons are charge particles their energy can be controlled by passing the beam through a controllable potential difference.
The system disclosed in that patent can identify substances such as explosives or narcotics by detecting resonances indicating the presence of nuclei included in a substance to be detected. However, because of the requirement of tuning the energy of the neutron beam, the source requires electrical power and circuitry to control the potential difference applied to the proton beam. Thus, it would not be suited for use in a hand-held, portable device.
Other non-destructive search methods include the use of animals, sniffers, nuclear magnetic resonance, gamma ray scattering, and ultrasonics. Both animals and sniffers are unable to detect narcotics in hermetically sealed containers. Gamma rays and NMR are not effective to penetrate metal barriers. Ultrasonics is useful for probing liquid containers but not as effective otherwise.